As industrialization advances, environmental pollution becomes more severe, and people are paying more attention to their living environments. Accordingly, air purifiers which purify indoor air are becoming more popular. An air purifier sucks in ambient air by an air intake fan, purifies the sucked air by a filter element, and then outputs the purified air by an air discharging fan. Users can insert different filter elements in the air purifier to meet various demands, such as dust filtering and deodorization. However, in the related arts, it is difficult to measure purification parameters of air purifiers.